Burner with air flow adjustment

A method of designing a contoured peripheral surface of an air flow restrictor for use in a burner so as to reduce a first blower pressure P1 upstream of said air flow restrictor in a direction of air flow in the burner to a prescribed pressure P2 between said air flow restrictor and a burner head at an adjustment range of said air flow restrictor between a minimum air flow position and a maximum air flow position, said air flow restrictor comprising one component comprising said contoured surface and another component comprising a throttle plate having a peripheral surface, one of said components being movable relative to the other, said method comprising the steps of:

• measuring performance data of the burner;
• selecting a radius R1 of said throttle plate;
• selecting an area of apertures in said throttle plate which provide air for a low firing rate at the minimum air flow position;
• calculating a minimum of a radius R2 of said contoured surface which occurs when said throttle plate is located at the minimum air flow position, using the equation, R2=(AV1/π+R12)½, where AV1=a calculated annular clearance area between said throttle plate and said contoured surface based upon said performance data,
• determining a shape of said contoured surface comprising the steps of:
• (a) assuming a plurality of small incremental adjustments of said movable component from the minimum air flow position toward the maximum air flow position along the central axis resulting in a segment at each increment on a reference line along the central axis,
• (b) locating a transverse line S at the start of a segment at an angle θ between said transverse line S and said reference line which is perpendicular to a section of said contoured surface corresponding to a prior segment nearer to said minimum flow position, said transverse line S being positioned to extend from the reference line,
• (c) inserting the angle θ into a trigonometric function as to the equality of R2 in which the transverse line S is an unknown,
• (d) determining a length of the transverse line S by substituting the equation resulting from step (c) into the equation, π·S·(R1+R2)=QV1/(CV1·Ve1), where QV1, AV1 and Ve1 utilize said measured performance data and QV1=an air flow rate through said annular clearance area AV1, CV132 a discharge coefficient of said annular clearance area AV1, and Ve1=the air velocity generated by P1-P2, thereby determining the coordinates of a point at said contoured surface,
• (e) repeating steps (b) through (d) to determine all of the points desired at said contoured surface.

A burner comprising:

• a motor driven blower;
• an air tube having an inlet end portion and an outlet end portion;
• a blower housing forming an air flow path between said blower and said air tube;
• a nozzle for spraying liquid fuel toward the outlet end portion of said air tube;
• a conduit for feeding the fuel to said nozzle;
• a two-stage air control device comprising a first air flow restrictor disposed upstream of said nozzle in the air tube relative to a direction of air flow and a second air flow restrictor disposed near said nozzle;
• linking structure that operatively connects said first air flow restrictor and said second air flow restrictor together;
• and
• a mechanism adapted to adjust the position of both said first air flow restrictor and said second air flow restrictor to control air pressure and flow rate with a single adjustment;
• wherein said first air flow restrictor is configured and arranged relative to said second air flow restrictor so as to reduce a blower pressure P1 upstream of said first flow restrictor to a lower throttled pressure P2 between said first air flow restrictor and said second air flow restrictor for each setting of said mechanism between a minimum setting and a maximum setting, said first air flow restrictor comprising a central throttle member and a throttle ring disposed around said throttle member which are movable relative to each other, one of said throttle member and said throttle ring being a perforated plate and the other of said throttle member and said throttle ring comprising a contoured peripheral surface,
• wherein slopes of said contoured surface and the size of a periphery of said plate form an aperture of various widths therebetween upon relative movement of the throttle member and throttle ring, which is effective to enable the blower pressure P1 to drop and the air flow rate to increase essentially uniformly with an adjustment in a setting of said mechanism while the throttled pressure P2 follows a prescribed value for each air flow rate and corresponding fuel flow rate of the burner.